Primary Deformation Zone Research Articles

Study on Extraordinarily High-Speed Cutting Mechanics and Its Application to Dry Cutting of Aluminum Alloys with Non-Coated Carbide Tools

The friction/adhesion between the tool and chip is generally large in metal cutting, and it causes many problems such as high cutting energy/rough surface finish. To suppress this, cutting fluid and tool coating are used in practice, but they are high in energy/cost and environmentally unfriendly. Therefore, this paper investigates the extraordinarily high-speed cutting (EHS cutting) mechanics of mainly soft and highly heat-conductive materials and proposes their application to solve the friction/adhesion problem in an environmentally friendly manner. In order to clarify the EHS cutting mechanics, a simple analytical model is constructed and experiments are conducted with measurement of the cutting temperature and forces. As a result, the following points are clarified/found: (1) heat softening at the secondary plastic deformation zone rather than the primary plastic deformation zone, (2) friction coefficient drop to 0.170 in EHS cutting, and (3) gradually increasing trend of cutting temperature in EHS cutting. Finally, EHS cutting is applied to dry cutting of aluminum alloys with a non-coated carbide tool and compared to conventional wet cutting with a DLC-coated carbide tool, and it is shown that a coating/coolant can be omitted in this region to achieve environmentally friendly cutting.

The influence of heat treatment process on the dynamic recrystallization evolution mechanism of Inconel 718 during high-speed machining

This study aims to investigate the cutting mechanisms of Inconel 718 alloy under different heat treatment processes and the grain refinement patterns of the transformed layer. By establishing a constitutive model suitable for cutting and importing it into DEFORM-3D for heat treatment processing and single-factor cutting experiment simulation, the effects of heat treatment processes and cutting parameters on cutting force, cutting temperature, and surface grain refinement were studied. The results indicate that the increase in cutting force is maximum, approximately 12 %, after the aging temperature is raised from 668 °C to 718 °C. The cutting force generated after aging heat treatment shows a negative correlation with cutting speed, whereas the cutting force after solution heat treatment rises significantly between 1400 and 1600 mm/s. The maximum cutting temperature occurs in workpieces after solution heat treatment, about 112 % of that of workpieces treated at 718 °C aging heat treatment. At the onset of cutting, the size relationship of the original grain volume is as follows: untreated < solution heat treatment < aging heat treatment; the number of nucleation points for dynamic recrystallization at grain boundaries is as follows: aging heat treatment < solution heat treatment < untreated. The most significant increase in the number of dynamic recrystallizations is observed after aging heat treatment at 621 °C, with the relationship of the number of recrystallizations in different cutting deformation zones being: secondary deformation zone < primary deformation zone < tertiary deformation zone. With the increase in cutting depth, the grain size of the workpiece after solution heat treatment first increases then decreases during the cutting process; the grain size of the workpiece after aging heat treatment first decreases then increases. The grain size of the workpiece during the cutting process after heat treatment is negatively correlated with cutting speed. Specifically, when the cutting speed is 600 mm/s, the grain size after solution heat treatment is the largest, about 1.1 times that of the 718 °C aging heat-treated workpiece.

The influence of microtexture tools on the geometric morphology of serrated chips based on stress triaxiality

PurposeThis study aims to investigate the effect of microtextured tools on the geometric morphology of serrated chips, and further improve the cutting performance of polycrystalline cubic boron nitride (PCBN) tool and extend the tool life and the surface quality of the machined surface.Design/methodology/approachA three-dimensional finite element cutting model of hardened steel AISI D2 with microtextured PCBN tools were established using the finite element software Abaqus, and cutting tests were carried out. Furthermore, the stress distribution in the primary deformation zone was investigated based on the triaxiality of stress, and the influence of microtexture on the geometric morphology of serrated chips and crack development was researched.FindingsThe results show that compared with nontexture tools, elliptical pits and wavy grooves microtexture tools have lower serrated degree Gs, higher serrated frequency f per unit length and more miniature serrated step Pc. The serrated phenomenon is intensified because the tensile stress zone of chips generated by nontextured tools is longer than that of elliptic pits and wavy grooves microtexture tools. Simultaneously, the maximum value of triaxiality in the tensile stress zone achieved by nontexture tools is larger than that of the two microtexture tools, and chips obtained by nontextured tools are more susceptible to propagation fractures.Originality/valueThis paper mainly studies the effect of microtexture on chip microgeometry, which is relatively little studied at present. At the same time, this paper has a certain engineering significance for PCBN tool turning hardening steel.Peer reviewThe peer review history for this article is available at: https://publons.com/publon/10.1108/ILT-05-2023-0149/

Chip formation mechanism in cryogenic machining of high temperature alloy-Inconel 718 and Ti-47.5Al-2.5V-1.0Cr

Inconel 718 and TiAl alloy are typical difficult-to-cut materials for their high cutting temperature, and cryogenic machining is an effective method to solve this problem. In order to reveal the material removal mechanism of these two materials in cryogenic machining, turning tests with different cooling media were designed and carried out. Cryogenic cooling could increase the brittleness of the material, making the material removal mechanism change from ductile removal to brittle removal. Due to the different plasticity of the material and their different sensitivity to temperature, the cooling conditions have slightly different effects on in the change of the removal mechanism of these two materials. By observing the geometric characteristics of chip, the deformation mechanism of the material near the chip free surface area was studied. Besides, the variation of chip root morphology was discussed to reveal the deformation mechanism of the primary deformation zone near the cutting edge. The experimental results showed that cryogenic cooling could change the material removal mechanism, but the sensitivity of different materials to temperature also have a significant influence, and the more sensitive to temperature, the more the material removal mechanism changes. The formation mechanism of serrated chips of Inconel 718 in cryogenic cutting was a combined action of ductile-brittle mixed fracture near the chip free surface and adiabatic shearing near the cutting edge. And the formation mechanism of Ti-47.5Al-2.5V-1.0Cr serrated chips is a combined action of periodic brittle fracture near the chip free surface and ductile-brittle fracture near the cutting edge.

In-situ DIC measurement of material deformation through spatial–temporal kinematics analysis during orthogonal cutting Ti6Al4V

A strong relationship exists between material deformation and cutting conditions in machining process. The continuous material deformation behaviors temporally varying in shear zone are required to be in-situ measured during machining. The spatio-temporal kinematics for material deformation with in-situ DIC measurement during orthogonal cutting Ti6Al4V is proposed. The image processing, digital image correlation and high-speed photography techniques are presented to analyze spatial–temporal kinematics of material plastic deformation during orthogonal cutting Ti6Al4V. The post-processing imaging technique is developed to process raw image sequences. The possessed image quality is characterized by four indicators. The evolution of material deformation along different strain paths is captured and analyzed in adiabatic shear bands. The spatio-temporal kinematic fields within the primary shear deformation zone under different cutting conditions are investigated by experiments. The research results can help to more precisely understand the dynamic mechanism of material plastic deformation during the manufacturing process.

Regime features of austempered ductile iron cutting

Machining regimes and sub-regimes of dry straight finish-turningof structural austempered ductile iron (ADI) with low cBN-content PcBN-based cutting inserts were examined. The global and local characteristics of TC contact and chip formation processes tied to this turning, as estimated by Katuku [Journal of Manufacturing Processes 78, 2022, 288–307], were used in this attempt. The significance of each prominent feature of these regimes was discussed from multiple perspectives. Across primary deformation zones (PDZs) and secondary deformations zones (SDZs), drag-controlled (or shock-induced) and defect-controlled plasticity regimes are, in turn, dominant and secondary. Coupled shear localisations in PDZs and SDZs occur via strain softening for cutting speeds beyond ~175 m min−1. BUE softening turns active at ~650 °C (~125 m min−1). Two bordering machining regimes emerged in close link with this cut-off temperature alongside a ⁓16 % cut-off SDZPDZ softening-degree, to name a few. Higher SDZPDZ softening-degree and moderately low mean contact stresses (high TC contact-length factor), TC contact temperature and sliding-friction coefficient, prevailing for Machining-regime-I (50–150 m min−1), hint at lower-pace wear regimes. The opposite conditions, standing for Machining-regime II (200–800 m min−1), suggest temperature-affected and stress-backed higher-pace wear regimes. Mean total energy levels (3476–7122 and 4364–4596 MPa) imply residual stresses built-up and microstructure damage below the machined surface. Machining sub-regimes are linked to solid-state phase transformations in PDZs/SDZs. Shear energy stored in PDZs/SDZs (166–291/1.5–43 MPa and 159–134/33–72 MPa) matches these transformations. Machining sub-regimes are sensitive to shallow variations in TC settings past ~175 m min−1. Powder lubrication by smeared-out graphite nodules is worthless in Machining-regime II. Cutting speeds of 150–400 m min−1 (TC contact temperature of ~685–930 °C and chip compression ratio of 3.4–2.32), sampled at the confluence of Machining-regimes I and II, are recommended for dry straight finish-turning structural ADI with low cBN-content PcBN-based cutting inserts.

Dual-scale folding in cutting of commercially pure aluminum alloys

We examine a, hitherto, little-studied and curious machining chip morphology, with tell-tale signs of folding at two different length scales, that is common in cutting of certain ductile and highly strain-hardening metals like soft aluminum alloys, tantalum and niobium. This chip morphology does not appear in the usual catalogues of common chip types. The mechanics of formation of the “dual-scale folded chip” is studied in model material systems of commercially pure aluminum alloys (AA 1100 and AA 8040), that prominently exhibit this chip morphology. The flow, folding and associated plastic instabilities are investigated using micro/macro structure observations of the chip in a plane-strain cutting framework, with high-speed in situ imaging and image analysis of material flow; and force measurements. The smaller-scale folding is shown to develop in the primary deformation zone while the larger-scale folding occurs as the chip traverses the rake face of the tool. The resulting chip is composed of irregularly-spaced large folds, superimposed onto which are the quasi-periodic small folds. The representative wavelengths of the two folds differ on average by an order of magnitude, 0.1 mm vs. 2 mm. The observations reveal a direct coupling between the material flow and chip morphology, and how specific attributes of the dual-scale folded chip arise from the flow mechanism. Plastic buckling is found to play a key role in the folding at both length scales. The small-scale folds are characteristic of a sinuous plastic flow mode, while the large-scale folding is characterized by buckling and stick-slip along the tool rake face, triggered by adhesive pinning of the chip to the tool. Important consequences of the dual-scale folding are very large cutting forces, and force oscillations of large amplitude, despite the alloys being very soft, only ∼25 HV. The dual-scale folding is why many of these alloys are classified as “gummy” to machine. Since the dual-scale folded chip is associated with large cutting forces and poor surface quality, there is much to be gained by disrupting this flow type in practical machining applications. Methods for controlling the folding to improve machining performance with the gummy alloys are briefly discussed.

Orthogonal Cutting Force Modeling Using the Nonequipartition Parallel Shear-Zone Distribution Model

This paper proposed a modified Oxley’s model using the nonequipartition parallel shear-zone theory. By introducing a strain and strain rate distribution model in the first shear band, the assumption that primary deformation zone was divided equally by the main shear plane was eliminated. Then the expressions of shear-zone thickness and resultant angle were derived according to Oxley’s cutting theory. Finally, a force prediction model for orthogonal cutting was established by analyzing the mechanical-thermal characteristics in the deformation zone. The thin-walled cylinder made of AISI 304 was used to carry out the orthogonal turning experiment. A variety of cutting force prediction models were used to compare with the experimental results. The calculation results from the proposed model show that the prediction accuracy of cutting force in both cutting and feed directions is improved.

Деформации в нестационарной стадии прессования прутка из алюминиевого сплава с малым коэффициентом вытяжки

Introduction. It is noted that extrusion is the main procurement process in the aluminum alloys forming operations. At the same time, the process has such a disadvantage as the nonstationarity of the metal plastic flow. The work aim is to establish the inhomogeneity deformation level of the pressed rod front part by numerical simulation using the finite element method. The study objectives are to formulate the extrusion process boundary conditions, to obtain a solution and to evaluate the inhomogeneity degree. Research methods: the finite element method was used to evaluate the deformed state. The actions sequence included the creation of primary deformation zone shape and the tool configuration. The mutual movement of the tool and the deformable material is set using the appropriate boundary conditions. The deformable medium is a ductile material with power-law hardening, the physical and mechanical properties correspond to the aluminum alloy of the 6000 series. Results and discussion: It is revealed that the strain degree in the pressed rod front part is extremely nonuniform distributed; differences above 300% are recorded. The strain degree distribution dependences in the rod cross sections are constructed depending on the distance from the front end at different relative radial coordinates. It is revealed that the rod central layers acquire a constant level of the strain degree earlier than the peripheral layers. The stationary process is achieved with less metal motion. The work result application scope is the technological study of rational metal cutting of aluminum alloys at the extrusion final stage in order to use recyclable waste more rationally. Conclusions. In the extrusion process with a low elongation ratio, the strain degree is distributed nonuniform both along the press rod cross and along its length. The rod front part remains weakly deformed both at the periphery and in the center in the nonstationary initial extrusion stage. It often forces to send for remelting due to the insufficiently developed metal structure. At the same time, if the limits on the minimum possible degree of deformation are set, then using the results of the calculation by the finite element method, the minimum length of the metal to be removed can be set, thereby reducing the mass of waste sent for remelting.

On the function of lead (Pb) in machining brass alloys

Lead has traditionally been added to brass alloys to achieve high machinability, but the exact mechanisms at work are still debated. Lead-free brass alternatives could be developed if these mechanisms were better understood. Accordingly, machinability characteristics were investigated for two brass alloys with similar mechanical properties and phase composition, but with very different machining characteristics because one has 3 wt.% lead (CuZn38Pb3) while the other has only 0.1 wt.% (CuZn42). The effect of the lead was investigated using infrared temperature measurement, electron microscopy, secondary ion mass spectroscopy, quick-stop methods, and high-speed filming. Neither melting of lead nor its deposition on the tool rake surface takes place during machining thus confirming its limited lubrication and tribological effects. Instead, the main role of lead is to promote discontinuous chip formation. Lead deforms to flake-like shapes that act as crack initiation points when the workpiece material passes through the primary deformation zone. This effect prevents the development of stable tool–chip contact, thus lowering cutting forces, friction, and process temperature.

Tool-chip contact and chip formation in dry finish-machining of austempered ductile iron

Straight dry finish-turning of a structural grade of austempered ductile iron (ADI) using cBN-TiC cutting tools was analysed. The influence of cutting speed on the characteristics of the tool-chip (TC) contact and chip-formation processes was the focus of this research. Experimental and analytical procedures were used in this respect. An approach to estimate the TC sticking contact length and TC stress distribution index was built to complement them. The feed rate, nominal rake angle, and depth-of-cut were kept at 50 μm rev−1, −26°, and 200 μm, respectively. The cutting speed was varied in the range of 50–800 m min−1. Strain-rate effects on the shear flow stress of structural ADI overpower their antagonist temperature impacts drastically in primary deformation zones (PDZs) and gradually in secondary deformation ones (SDZs). Accordingly, TC sliding-friction coefficient rises with the mean TC homologous temperature. The mean total energy brackets nearly match the range of specific cutting resistance for grinding of cast‑irons, related to the uncut-chip thickness of 14.23 μm. The levels of TC equivalent contact-stresses and mean TC contact temperature vividly reveal the vulnerability of cBN-TiC cutting-inserts edges for cutting speeds past 200 m min−1. The distribution index of TC contact stresses settled between 0.96 and 0.58. SDZPDZ softening degree decreased with cutting speed, landing between 76 and ~0%. Two bordering machining regimes, features of abrupt variations of local and global characteristics of the TC contact and chip-formation processes, emerged from the evolution of chip morphology with cutting speed: I: 50–150 m min−1, II: 200–800 m min−1. The pairing of these characteristics made it possible to blend them effectively. A better-informed procedure to select feed rate and cutting speed was then suggested.

Modeling of strain gradient-dependent strengthening effect in grinding of boron-diffusion-hardened titanium alloy

In grinding of the boron-diffusion-hardened titanium alloy, with the grinding speed increasing, the strain gradient-dependent strengthening (SGS) effect of TiB whiskers would become obvious, resulting in an improvement of the surface quality. To explore such SGS effect of TiB whiskers, a novel model of the strain gradient-dependent strengthening effect in the primary deformation zone was developed, and then a novel specific grinding energy model was further proposed to quantitatively estimate such SGS effect of TiB whiskers. It indicates that the above two models can adequately demonstrate the SGS effect of TiB whiskers in grinding the borided titanium alloy. The results demonstrate that the grinding performance of the borided titanium alloy was dominated not only by the grinding speed but also by the TiB whiskers. Due to high grinding speed (about 120 m/s) inclining to cause the maximum undeformed chip thickness reduced, when it was closed to the size of TiB whiskers, the SGS effect of TiB whiskers would become obvious, leading to an improvement of surface quality. Furthermore, when the size of TiB whiskers was closed to the sub-micron-scale, the enhanced SGS effect of the sub-micro-sized TiB whiskers tends to generate, causing the surface quality further improved.

Microstructural modulation of TiAl alloys for controlling ultra-precision machinability

TiAl intermetallic alloys have attracted considerable attention in aerospace applications over the last few decades owing to their low density and superior mechanical properties at high temperatures. However, these alloys are also known as difficult-to-machine materials that hinder efficient manufacturing. This study presents a systematic investigation on the machinability of TiAl alloys with three types of microstructures obtained by different heat treatment parameters. These were classified as near-gamma (NG), duplex (DP), and fully lamellar (FL). The machinability was evaluated based on the cutting forces and machined surface roughness. The material with α2/γ lamellar structures (FL) exhibited the lowest cutting force (3.21 N). However, produced a rougher surface (80 nm Ra) as compared to the NG microstructure (4.69 N and 47 nm Ra). Electron backscattering diffraction (EBSD) evaluation of the primary deformation zone in the cutting chips revealed that insufficient heat energy was converted from plastic deformation for recrystallization or β+γ→α2 phase transformation to occur. This indicated that the deformation mechanisms were significantly dependent upon the plasticity. The NG microstructure demonstrated a higher degree of plasticity in the primary deformation zone, which was attributed to the combined effect of super-dislocation decomposition, ordinary dislocation slip, and refined mechanical twins with preferred orientation along the <112¯> {111} crystallographic orientation. Conversely, the FL microstructure exhibited brittleness during chip formation due to the weak bonding force between hexagonal α2 and tetragonal γ phases that led to preferential micro-cracking along each interface. Reducing the crystal orientation is conductive for improving machined surface quality. The notion of enhanced brittleness to explain the reduction in cutting forces due to the dissipation of energy through fracture was supported with numerical simulations. Microscopic evaluation was used to understand the deformation differences of the equiaxed γ grain and α2/γ lamellar microstructure during micro-cutting. Additionally, enhanced the understanding of the deformation mechanism of these multi-phase alloys.

Some studies on the machining behaviour of 316L austenitic stainless steel

The objective of the present study is to establish the machining behavior of 316L austenitic stainless steel. The dry turning of 316L austenitic stainless steel was done on a lathe. The machining chips were collected and were examined under the scanning electron microscope. The power law equation of the form σ = Kεn was established for this steel. The strength coefficient ‘K’ and the strain hardening exponent ‘n’ were incorporated to evaluate the von Mises stresses at various experimental conditions. Corresponding shear forces of the PDZ (primary deformation zone) were determined using the von Mises stresses (VMS). The second order regression model was established. The model correlated the shear forces with the machining parameters. The model indicated that the material retained the strain hardening at the lowest speed, feed and doc. The work hardening effect was operating at this machining condition with the negligible influence of the thermal softening. The model also indicated that the maximum shear forces are developed for the very high speed, feed and doc because of the higher work hardening at the high strain and high strain rate. This caused the formation of the saw tooth chips through the crack initiation for the higher work hardening state.

Machinability analysis of dry and liquid nitrogen\u2013based cryogenic cutting of Inconel 718: experimental and FE analysis

Inconel 718 is famous for its applications in the aerospace industry due to its inherent properties of corrosion resistance, wear resistance, high creep strength, and high hot hardness. Despite the favorable properties, it has poor machinability due to low thermal conductivity and high hot hardness. To limit the influence of high cutting temperature in the cutting zone, application of cutting flood is recommended during the cutting operation. Cryogenic cooling is the recommended method when machining Inconel 718. However, there is very limited literature available when it comes to the numerical finite element modeling of the process. This current study is focused on the machinability analysis of Inconel 718 using numerical approach with experimental validations. Dry and cryogenic cooling methods were compared in terms of associated parameters such as chip compression ratio, shear angle, contact length, cutting forces, and energy consumption for the primary and secondary deformation zones. In addition, parameters related to chip morphology were also investigated under both lubrication methods. Chip formation in cryogenic machining was well captured by the finite element assisted model and found in good agreement with the experimental chip morphology. Both experimental and numerical observations revealed comparatively less chip compression ratio in the cryogenic cooling with larger value of shear plane angle. This results in the smaller tool–chip contact length and better comparative lubrication.

Analytical modelling of the trans-scale cutting forces in diamond cutting of polycrystalline metals considering material microstructure and size effect

In diamond cutting of polycrystalline metals, the influence of size effect and microstructure on the cutting force is prominent due to the trans-scale variation of undeformed chip thickness (UDCT) from microscale to nanoscale. This study proposes a trans-scale cutting force model for diamond cutting of polycrystalline metals with the full consideration of microstructure, material elastic recovery, size effect and round-tool-edge effect. Specifically, by corelating micro-forming theory and crystal plastic theory, a hybrid slip-line model (HSLM) is developed to determine the flow stress in the primary deformation zone, which can quantify the influence of size effect and microstructure, such as grain size, grain boundary and crystal anisotropy, on flow stress. Then, the normal cutting force and frictional cutting force are determined by analysing the stress distribution and frictional states at tool-chip interface using a tool-chip contact model. The rubbing force induced by material elastic recovery at very small UDCT is determined based on indentation theory. Through diamond cutting of polycrystalline copper with different grain sizes, it is experimentally demonstrated that the proposed HSLM can capture the cutting mechanism transformation phenomenon from shearing (tensile stress) to ploughing (compressive stress) with increasing size factor. Besides, the proposed force model has the improved estimation accuracy compared with the conventional force models developed based on Johnson-Cook constitutive equation.

Analytical thermal model of orthogonal cutting process for predicting the temperature of the cutting tool with temperature-dependent thermal conductivity

High temperatures generated in cutting processes significantly affect the surface integrity of machined parts and tool wear, leading to workpiece thermal damage, tensile residual stresses in the workpiece and a reduction in tool life. In recent years, different analytical thermal models to predict cutting temperatures have been developed in literature based on 2D modeling of the cutting process and the assumption that thermal conductivities of workpiece and chip are not dependent on temperature. However, this dependence of conductivity on temperature may have a significant influence on predicted temperatures and must be taken into account. In this paper, a thermal model of the orthogonal cutting process that considers thermal conductivity of materials (chip and tool) to be dependent on temperature is developed. A linear variation of thermal conductivity with temperature is assumed for chip (workpiece) and tool materials. The model is based on application of: (1) the Kirchhoff transformation in order to convert the nonlinear heat conduction problem into a linear one, (2) the theory of moving and stationary heat sources in semi-infinite and infinite mediums in order to model primary and secondary deformation zones and (3) imaginary heat sources to meet adiabatic boundary conditions in the chip and tool. Imaginary heat sources were defined in the thermal model proposed in this paper in such a way that the effect of the tool-chip interface dimensions and of cutting tool width on the tool temperature could be taken into account. This allows the temperature on the rake face and lateral faces of the tool to be predicted. To this end, a new methodology that considers the temperature-dependent thermal conductivity of materials was developed in order to estimate heat partition ratio along the secondary heat source (tool-chip interface), which is assumed to be non-uniform. Orthogonal cutting tests were also performed in order to verify model predictions by comparing them to tool temperature distributions measured using an IR camera.

The Modulation Effect on the ELVEs and Sprite Halos by Concentric Gravity Waves Based on the Electromagnetic Pulse Coupled Model

By employing the finite-difference time-domain method, the processes of electric field variation and morphological development of the optical radiation field of ELVEs and sprite halos were simulated in this article. Simulations of ELVEs show two optical radiation field centers, with a concentrated luminous zone from 85 to 100 km and an inner weaker optical radiation center. The electric field exhibits an obvious sparse and dense ripple pattern induced by the concentric gravity waves (CGWs) at altitudes of 90–100 km, which mainly occurs during the decline period of electric field with a shallow steepness. The alternating distance of the variations in the sparse and dense patterns is about 40 km, which corresponds to the horizontal wavelength of the electric field. The CGWs induce significant deformation of the inner optical radiation field, even splitting into multiple luminous regions. Simulations of sprite halos indicate that the horizontal range of the electrical field generated by lightning current is within 50 km, and a strong local electric field formed in the region right above the lightning channel is due to the small-scale breakdown current. Thus, the increased electron density shields the upper regions and reduces the electrical field’s strength. The sprite halos luminous zone is pancake-shaped, and it originates at 85 km along with a downward developing trend. The disturbance of sprite halos’ luminescence caused by CGWs mainly occurs at about 80–100 km directly above the lightning channel, and the primary deformation zone is located within 30 km of the lightning channel, which is also the region with the most recognizable electric field disturbance.

Effect of cutting speed on surface integrity and chip formation in micro-cutting of Zr-based bulk metallic glass

Single-shear plane theory is an effective tool for understanding the cutting mechanisms of conventional and precision machining. This study investigates the formation of multiple shear bands in micro-cutting of zirconium-based bulk metallic glass (BMG) where classic models have not been studied. A series of slip steps were observed in the cutting direction which was significantly affected by cutting speed. Surface roughness of the machined surface in micro-cutting BMG was found to be sensitive to the cutting speed. Electron microscopy studies further confirmed the mechanism of the micro-cutting-induced nanocrystallization with the formation of shear bands within the primary deformation zone in the micro-cutting process under various cutting speeds. This work contributes to demonstrating the effects of cutting speed on the formation of the shear band and the serrated flow behavior under complex loading and boundary conditions in micro-cutting.

Chip formation mechanism during orthogonal cutting of rubber microparticles and silica nanoparticles modified epoxy polymers

The addition of well-dispersed nanoparticles can significantly increase the mechanical properties and toughness of epoxy polymers. In this study, an epoxy resin was modified by addition of silica nanoparticles, (CTBN) rubber microparticles and a combination of both. An in-situ orthogonal cutting rig combined with high magnification and high-speed imaging system was used to determine the effects on the chip formation mechanism and machining induced damage to the material. This study indicates that chip formation in silica-modified epoxy is governed by a fracture process with large cracks both at the machined surface level and subsurface within the chip formation zone. The presence of rubber enables larger plastic deformation within the epoxy-modified polymer as the toughening mechanism of the rubber deflects the generated cracks within the primary deformation zone. The magnitude of machining induced damage was found to be lower for rubber microparticles and was correlated with a rubber toughening mechanism observed during cutting. The higher magnitude of machining induced damage of silica-modified epoxy was linked to the material’s poor resistance to crack initiation and growth. These findings of the effect of rubber microparticles and silica nanoparticles on chip formation process will give engineers a greater ability to create a trade-off between filler properties vs material properties vs machining induced damage during Design for Manufacturing (DFM) stages of a product design.